1. Field of the Invention
The present invention relates to a method and device for detecting deterioration of lubricating oil circulating in a gas engine for driving an electric generator to lubricate sliding surfaces in the engine and monitoring the lubricating oil deterioration, specifically to those with which deterioration of oil can be detected in real time.
2. Description of the Related Art
Gas engines for driving electric generators have an oil tank and oil supply device to supply lubricating oil to rotating parts and sliding parts in order to secure smooth movement of the parts preventing abrasion of them. The lubricating oil accumulated in the oil tank is supplied through oil path via an oil filter and oil cooler to pistons, cylinders, bearings, etc. for lubrication and cooling of them and returned to the oil tank to be again supplied to the parts to be lubricated.
The lubricating oil is exposed at high temperature and experiences mechanical stress in the gas engine and deteriorates, that is, viscosity and purity decreases. Therefore, it is necessary to change periodically the lubricating oil to new oil. To judge timing of changing oil, it is important to monitor deteriorated condition of the lubricating oil.
Conventionally, a method of judging degree of oil deterioration by periodically sampling lubricating oil from the engine and chemically analyzing the sample oil has been prevailed. However, considerable time is needed to obtain chemical analysis after sampling the lubricating oil, and it is hard to say changing oil has been done at proper timing. So, it has been demanded to develop a device able to detect deterioration of lubricating oil in real time.
A device for detecting deterioration of engine oil is disclosed in Document 1 (Japanese Laid-Open Patent Application No. 10-78402), with which change in electric property of oil due to deterioration is detected. According to the disclosure, a resistance sensor is provided in the oil sump of the engine to measure electric resistance of oil, and need of changing oil is informed to the operator when detected electric resistance of oil decreases to a prescribed value.
In Document 2 (Japanese Laid-Open Patent Application No. 2004-354082) is disclosed another example of device for detecting deterioration of engine oil. According to this invention, sensor for detecting oil deterioration is located in a main gallery where lubricating oil filtered via an oil filter passes to be supplied to sliding parts in the engine.
The oil deterioration detecting sensor is composed to have two electrodes facing each other with a certain distance to form a gap between the electrodes to constitute a condenser with lubricating oil flowing through the gap between the electrodes. Electric capacitance between the electrodes is measured by applying alternating voltage, and degree of deterioration is determined based on relative permittivity obtained from the measured electric capacitance.
However, with the art disclosed in the Document 1, degree of oil deterioration is judged based on decrease in electric resistance of the oil, which is susceptible to mixing of foreign matter such as carbon in the oil.
With the art disclosed in the Document 1, also the electric capacitance is influenced by temperature of the oil and foreign matter mixed in the oil, resulting in increased measurement deviation.
There are other methods of detecting deterioration of oil, for example, by measuring change in viscosity, change in light transmission, or change in pH of the oil, however, these measurements are also influenced by temperature of the oil or foreign matter in the oil, and proper judgment of degree of deterioration of oil has been not easy.